The present invention relates to a system for the incineration of combustible gases in a reaction chamber wherein the gas is introduced into the reactor in a low pressure laminar flow state. More particularly, the invention relates to a method of incinerating waste gases from industrial processes by substantially converting them to relatively non-polluting, low temperature products of combustion. Still more particularly, the invention relates to a means for combusting pyrophoric silane waste products from epitaxial or other reactors which are used in the manufacture of semiconductors.
Methods of incinerating gaseous waste products have been known heretofore. Generally, such have suffered from the disadvantage that substantially complete combustion of the vent gas has not been achieved, thereby allowing the release of pollutants to the atmosphere, or products of combustion result at unacceptably high temperatures. Also, the release of pyrophoric materials such as silanes is very dangerous since they may spontaneously ignite uncontrolledly when mixed with air. Further, apparatus for carrying out prior methods for incinerating streams of combustible vent gas are often relatively expensive to install and operate. In these cases, the waste gases are introduced into a reaction chamber under relatively high pressure either via pumping or nozzle means in order to intimately mix with incoming air for subsequent ignition. Such high pressure systems are not suitable for some industrial processes. For example, in the manufacture of semiconductors, silane gas along with other components such as phosphine and arsine are conducted over silicon wafers for reaction therewith. In order to assure a highly uniform wafer, the reactants are introduced at about atmospheric pressure or very slightly above atmospheric pressure which is sufficient only to insure flow into the reactor. Waste gases from this reactor exit at essentially the same rate as the inflow. Inflow is naturally laminar to assure uniformity of production and therefore waste gases exit through appropriate piping in a laminar fashion. Should the exit flow be subsequently constricted, for example via a nozzle, to raise the velocity of exiting gases to induce turbulent flow for mixture with air, then an unacceptable back pressure would be induced upstream in the silane/silicon wafer reactor. Furthermore, it is theorized, that when turbulent silane gas is admixed with air it is atomized thus forming a protective invisible bubble of silicon dioxide around molecular silane. When this bubble is burst in uncontrolled surroundings, it reacts with air explosively with much resultant property damage or even death. The present invention either effectively prevents bubble formation or shears these bubbles open in a controlled combustion chamber and ignites the silane gas to form relatively harmless and non-polluting oxides of silicon.